There have been widely used, for example, corrugators or corrugating equipment in which a corrugating medium is manufactured so a to have corrugations with a desired pitch size. The medium is then glued together with a liner across the crests of the corrugations using an adhesive so as to form a single-faced corrugated board sheet. The resulting single-faced corrugated board sheet is then adhesively bonded with a back liner so as to form a double-faced corrugated board sheet. In such type of corrugators, cardboard web feeding devices, for rotatably supporting rolls each of which comprises a core tube having wounded thereon a cardboard web such as, for example, a corrugating medium, liner and back liner (these cardboard webs are hereinafter referred to as a "web"; and a roll having such a web wound thereon is hereinafter referred to as a "web roll") so as to feed webs therefrom, are indispensable.
As a prior art web feeding device to be employed within a corrugator, a mill roll stand having a so-called swing arm system as shown in FIG. 6 is widely known. The mill roll stand shown with the numeral 10 comprises two pairs of swing arms 13, each pair comprising a right arm and a left arm which are connected to horizontal pivotal shafts 11 and 12, respectively, by means of splines. The respective arms 13 have a center block 16 at the inner end thereof such that it may oppose its counterpart provided upon the other arm 13, and can be fitted into the end portions of a core tube 15 of a web roll 14. A transportation means 17 comprising a flat car or the like for transporting the web rolls 14 into and out of the corrugator equipment is provided at a position below the swing loci of the respective pairs of swing arms 13.
In order to achieve the loading of a web roll 14 onto one pair of swing arms 13 supported, for example, upon the right side pivotal shaft 12 within the mill roll stand 10, the transportation means 17, having had a web roll 14 loaded thereon at a specified stockyard is allowed to travel until it reaches below the swing loci of the swing arms 13, at which time the swing arms 13 are laterally spaced from each other, and in this state the right side pivotal shaft 12 is pivoted or rotated in the clockwise direction until the center blocks 16 are coaxially aligned with the axis of the core tube 15 of the web roll 14.
Subsequently, the swing arms 13 are moved closer to each other along the common axis thereof so as to effect chucking of the core tube 15 of the web roll 14 by means of the center blocks 16, and then the arms 13 are swung in the counterclockwise direction whereby loading of the web roll 14 (also referred to as the "web setting" operation) is achieved.
There is occasionally employed a mill roll stand which includes a turn-over system in which arms extending from the pivotal shaft in the opposite directions swing integrally, or alternatively, there may be employed a system in which a pair of bases disposed upon an endless route are moved by means of an endless chain, in addition to the mill roll stand having the swing arm system described above. In any case, loading and unloading of the web rolls is designed to be achieved by moving a pair of center blocks disposed upon the arms or the bases toward or away from each other with the axes thereof being aligned. When the web roll 14 carried upon the transportation means 17 is to be loaded upon the swing arms 13 of the mill roll stand described above, the center blocks 16 are required to be axially aligned with the axis of the core tube 15 of the web roll 14.
In order to achieve the aforenoted alignment, the axis of each center block 16 travels along the arcuate locus to be traversed by pivoting the swing arm 13 around the axis of the pivotal shaft 12, with the length of the swing arm 13 defining a radius, and consequently, it is not always possible to align the axis of the web rolls 14 having different roll diameters with the axis of the center blocks 16. Accordingly, the operation of centering the center blocks 16 with respect to the core tube 15 has been achieved manually thereby causing automation of this operation to be effectively disregarded.
Moreover, when a web roll 14 has a considerably reduced diameter after consumption of the web as shown in FIG. 7, automatic loading of the web roll is not feasible. More particularly, a brake means 18 is coaxially disposed with respect to the center block 16 attached at the tip of the swing arm 13 for preventing over-run of the web, which may be caused by means of the inertia generated during the rotation of the web roll 14, the same exerting a braking force with respect to the rotation of the center block 16. The brake means 18 may have a considerably large diameter due to its structure, so that its closest approachable distance to the factory ground surface may naturally be limited, thereby preventing it from properly engaging or supporting the core tube of the web roll 14 along the axis of the core tube of the web roll 14 with respect to the transportation means 17, which has a considerably reduced diameter after consumption of the web.
Since automatic chucking by means of the center blocks is feasible under such conditions, difficult manual labor must be exerted by means of the operators in elevating the web roll 14 so as to set the end portions of the core tube 15 upon the center blocks 16. Furthermore, this operation of exchanging web rolls 14 takes considerable time, leading to a disadvantageous reduction in the operational efficiency.
For the purpose of overcoming such problems an invention entitled "Web Feeding Device for Corrugator" has been proposed by the present applicant and filed as Japanese Patent Application No. 221623/1987. The device according to this invention is designed such that a web roll may be elevated by means of a lifter disposed below the swing loci of the swing arms. Accordingly, irrespective of the size of the web roll diameter, the center blocks and the axis of the core tube of the web roll can be aligned so as to allow automatic chucking, and therefore, the time for completion of the roll exchange operation can be minimized. However, in today's corrugated board manufacturing industry where there is a necessity to cope with frequent order changes associated with small lot productions, a further reduction of the cycle time for the web roll exchange operation is desired.